Audio Recording Equipment
Audio Recording Equipment covers the chain from transducer to storage and the numbers that keep it clean: levels, impedance, sampling, bit depth and file size. The exam tests practical gain-staging and whether you can justify a sample rate or bit depth rather than recite it.
The signal chain
- Source, microphone or DI, microphone preamplifier, analogue-to-digital converter, recorder or computer, monitoring.
- Level families: microphone level (about −60 dBu), professional line level (+4 dBu), consumer line level (−10 dBV), and instrument level delivered to a high-impedance DI.
- Balanced connections (XLR, TRS) use two signal conductors plus screen and cancel induced noise; unbalanced (TS, RCA) are prone to hum over long runs.
- Phantom power is +48 V DC on pins 2 and 3 of an XLR, used by condenser microphones; it can damage some ribbon microphones.
Digital conversion
- Nyquist theorem: the sample rate must exceed twice the highest frequency, so 44.1 kHz captures up to about 22 kHz; 48 kHz is the video standard; 96 kHz is used for high-resolution work.
- Word length sets dynamic range, roughly 6 dB per bit: 16-bit ≈ 96 dB, 24-bit ≈ 144 dB.
- Headroom prevents clipping; record peaks around −12 to −6 dBFS, then normalise later.
- Dither is low-level noise added when reducing word length to avoid quantisation distortion.
- Common formats: WAV/BWF uncompressed, MP3 and AAC lossy, FLAC lossless compression.
Worked example. Size of 60 s stereo 48 kHz/24-bit WAV: 48,000 samples × 3 bytes = 144,000 bytes per second per channel; × 2 channels = 288,000; × 60 s = 17,280,000 bytes, about 17.3 MB.
Traps
- Applying phantom power to a ribbon microphone or to an unbalanced consumer device.
- Confusing sample rate (bandwidth) with bit depth (dynamic range).
- Recording too hot and trusting later repair; clipping cannot be undone.
- Mixing dBu, dBV and dBFS in level-budget questions.